46 BIOLOGICAL SOCIETY OF WASHINGTON. 



his line of argument carried to its extreme logical conclusion 

 would not preclude the possibility of any variation whatever 

 even in the germ-plasms themselves. It is not sufficient to say 

 that all variation is due to the varied character of multitudin 

 ous germ-plasms in the fertilized ovum, brought there from 

 many often remote ancestors possessing very different charac 

 ters. This is a petitio principii, since it assumes these differ 

 ences in those ancestors, and the primary question must be 

 answered ; whence these ancestral differences ? How does he 

 account for any differences at all ? 



'We have already seen that Weismann restricts his denial 

 to multicellular organisms and admits as a necessary part of 

 his theory, that unicellular organisms are easily affected by 

 the nature of their surroundings and activities, and that the 

 changes thus produced are directly transmitted. " If for in 

 stance," he says, "a protozoan, by constantly struggling 

 against the mechanical influence of currents in water, were to 

 gain a somewhat denser and more resistent protoplasm, or were 

 to acquire the power of adhering more strongly than the other 

 individuals of its species, the peculiarity in question would be 

 directly continued on into its two descendants, for the latter 

 are at first nothing more than the two halves of the former. 

 It therefore follows that every modification which appears in 

 the course of its life, every individual character, however it 

 may have arisen, must necessarily be directly transmitted to 

 the two offspring of a unicellular organism (p. 278). . . . We 

 are thus driven to the conclusion that the ultimate origin of 

 hereditary individual differences lies in the direct action of ex 

 ternal influences upon the organism " (p. 279). But he even 

 goes further and asserts that there is no other way by which 

 the germ can be affected. " I have never doubted" he says, 

 1 ' about the transmission of changes which depend upon an 



